U.S. patent number 6,936,300 [Application Number 09/935,332] was granted by the patent office on 2005-08-30 for method for fabricating organic electroluminescent display.
This patent grant is currently assigned to Samsung SDI Co., Ltd.. Invention is credited to Tae Min Kang, Jang Hyuk Kwon, Seong Taek Lee, Joon Young Park.
United States Patent |
6,936,300 |
Lee , et al. |
August 30, 2005 |
**Please see images for:
( Certificate of Correction ) ** |
Method for fabricating organic electroluminescent display
Abstract
Relating to a method for fabricating an organic
electroluminescent display having improved surface flatness and
thickness uniformity as well as an improved image quality at edge
regions of a pattern, a method for fabricating an organic
electroluminescent display includes the steps of: forming a first
electrode layer on a transparent substrate, the first electrode
layer being a positive electrode; forming an assistant layer on the
first electrode layer; forming an organic luminescent layer on the
assistant layer by scanning a donor film using a laser beam, the
donor film being disposed on the substrate having luminescent
materials for R, G, and B; removing the donor film; and forming a
second electrode layer on the organic luminescent layer, the second
electrode layer being a negative electrode, wherein the step of
forming an organic luminescent layer comprises the step of
dithering the laser beam in a direction perpendicular to a scanning
direction of the laser beam.
Inventors: |
Lee; Seong Taek (Suwon,
KR), Kwon; Jang Hyuk (Suwon, KR), Kang; Tae
Min (Suwon, KR), Park; Joon Young (Seoul,
KR) |
Assignee: |
Samsung SDI Co., Ltd.
(Suwon-si, KR)
|
Family
ID: |
36751862 |
Appl.
No.: |
09/935,332 |
Filed: |
August 23, 2001 |
Foreign Application Priority Data
|
|
|
|
|
Aug 24, 2000 [KR] |
|
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2000-49287 |
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Current U.S.
Class: |
427/66; 427/555;
427/596; 427/68 |
Current CPC
Class: |
H01L
51/0009 (20130101) |
Current International
Class: |
H01L
51/05 (20060101); H01L 51/40 (20060101); B05D
005/06 (); B05D 005/12 () |
Field of
Search: |
;427/66,68,555,596 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Cleveland; Michael
Attorney, Agent or Firm: Stein, McEwen & Bui, LLP
Claims
What is claimed is:
1. A method for fabricating an organic electroluminescent display,
comprising: forming a first electrode layer on a transparent
substrate; forming an organic luminescent layer on the first
electrode layer by scanning a donor film disposed on the substrate
using a laser beam; removing the donor film; and forming a second
electrode layer on the organic luminescent layer, wherein the laser
beam is a complex laser formed by mixing a plurality of lasers
having different energy distributions.
2. The method of claim 1, wherein the organic luminescent layer is
formed of a poly phenylene vinylene (PPV)-based material or poly
fluorine (PF)-based material.
3. The method of claim 1, wherein the complex laser beam has a
section formed in an oval-shape having a longitudinal diameter
greater than a lateral diameter, the longitudinal diameter is
formed in a scan direction.
Description
OBJECT OF THE INVENTION
[Field of the Invention and Description of the Related Art]
The present invention relates to a method for fabricating an
organic electroluminescent display, and more particularly, to a
method for fabricating an organic electroluminescent display having
improved surface flatness and thickness uniformity as well as an
improved image quality at edge regions of a pattern.
An electroluminescent display includes an electroluminescent
material disposed between electrodes, and is designed to realize an
image by applying a voltage to the electrodes so as to form an
electric field therebetween such that the electroluminescent
material may become luminescent. Such an electroluminescent display
is classified into an inorganic electroluminescent display and an
organic electroluminescent display depending on the
electroluminescent material. The inorganic electroluminescent
display has been put into practical use and is widely used for a
backlight of a watch, and the organic electroluminescent display is
under strong investigation since it shows merits of high luminance
and efficiency, drivability by a low voltage, and high
responsiveness, in comparison with the inorganic one.
Generally, such an organic electroluminescent display includes a
transparent substrate, on which an anode electrode, an organic
luminescent layer, and a cathode electrode are consecutively
disposed.
The organic luminescent layer may have a variety of structures
depending on an electroluminescent material. For example, the
organic luminescent layer may be formed of a hole transport layer,
an luminescent layer, and an electron transport layer, or of a hole
transport layer and an electron transport/luminescent layer, or of
a hole transport/luminescent layer.
In the above described organic electroluminescent display, the
organic luminescent layer is designed to realize red (R), green
(G), and blue (B) colors so that it can be applied to a color
display.
Such an organic luminescent layer is generally formed through a
vacuum evaporative deposition process using a shadow mask or
through a conventional optical etching process. However, the vacuum
evaporative deposition process has a limitation in reducing the
physical gap between the patterns and it is difficult to form a
minute pattern to tens of .mu.m level which is required against the
possible deformation of the mask. When the optical etching process
is applied, although it is possible to form the minute pattern,
practical application becomes difficult since the property of the
luminescent material forming the organic luminescent layer may be
deteriorated by the developing solution or the etching
solution.
Therefore, a thermal transferring method that is a kind of dry
etching processes has been recently proposed to form the organic
luminescent layer.
The thermal transferring method converts light emitted from a light
source into thermal energy by which an image formation material is
transferred to a substrate to form a color pattern. Therefore, to
perform the thermal transferring method, a light source, a donor
film and a substrate are required.
That is, as for a brief description of formation of a color image
according to thermal transferring method, a light emitted from a
light source such as a laser is scanned on a donor film to be
absorbed by absorbent of the donor film such that the light becomes
converted to thermal energy, and color material of the donor film
is transferred to a surface thereof by the thermal energy.
Actually, according to the thermal transferring method, a color
image is formed by scanning a laser beam of a desirably adjusted
focus to the donor film disposed on the substrate according to a
desired pattern.
For an example of such a prior art, U.S. Pat. No. 5,521,035
discloses a method for fabricating a color filter for a liquid
crystal display through a laser thermal transferring process.
In this patent, the color filter is fabricated by a laser induction
thermal transferring process for transferring a color material from
a donor film to a substrate such as a glass or a polymeric film. As
a laser unit, an Nd:YAG laser system is used for transferring the
color material to the surface of the substrate.
The Nd:YAG laser forms a Gaussian beam having a distribution of a
Gaussian function shape. When a diameter of the Gaussian beam is
set large (approximately, above 60 .mu.m), the inclination of the
energy distribution is slowly reduced as it goes away from the
center point.
Therefore, as shown in FIG. 2, when the Gaussian beam 110 having a
predetermined diameter is scanned in an X-direction as shown in
FIG. 2, since the beam intensity is low at the both edges of a
color pattern 112, the quality of the color pattern 112 at the both
edges is deteriorated when compared with the central portion.
[Object to be achieved by the present invention]
When the energy of the laser beam is intensified to improve the
image quality at the edges in order to solve the above problem,
although the image quality at the edges may be enhanced, the
surface of the image pattern becomes irregular since the energy is
excessively increased at the central potion.
At this point, the present invention has been made to solve the
problem, and an objective of the present invention it to provide a
method for fabricating an organic electroluminescent display having
an improved surface flatness and thickness uniformity as well as an
improved image quality at edge regions of a pattern
[Constitution and Operation of the Invention]
In order to achieve the objective, the present invention provides a
method for fabricating an organic electroluminescent display
wherein a laser beam is dithered in a direction perpendicular to a
scanning direction of the laser beam while forming an organic
luminescent layer on the assistant layer by scanning a donor film
using a laser beam, the donor film being disposed on the substrate
having luminescent materials for R, G, and B.
In addition, the present invention provides a method for
fabricating an organic electroluminescent display wherein a single
laser beam formed by a composition of a laser beam having gentle
inclination in energy distribution and a laser beam having steep
inclination in energy distribution such that inclination in energy
distribution is increased at a threshold energy is utilized while
forming an organic luminescent layer on the assistant layer by
scanning a donor film using a laser beam, the donor film being
disposed on the substrate having luminescent materials for R, G,
and B.
Thereby, thermal transferring at a pattern edge of an organic
luminescent layer is ensured.
Preferred embodiments of the present invention will be described in
detail with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph for illustrating an energy distribution of a
laser beam used for a conventional thermal transferring method.
FIG. 2 is a schematic view for illustrating a method for forming a
pattern using a conventional thermal transferring method.
FIG. 3 is a block diagram for illustrating a method for fabricating
an organic electroluminescent display.
FIG. 4 is a schematic view of an organic electroluminescent display
fabricated according to a method shown in FIG. 3.
FIG. 5 is a schematic view for illustrating a method for
fabricating an organic electroluminescent display according to a
first embodiment of the present invention.
FIGS. 6 to 8 are schematic views for illustrating dithering
examples of a laser beam used for the present invention.
FIG. 9 is a graph for illustrating a sectional energy distribution
of a laser beam used for the present invention.
FIG. 10 is a schematic view for illustrating a method for
fabricating an organic electroluminescent display according to a
second embodiment of the present invention.
FIG. 11 is a schematic view for illustrating a method for
fabricating an organic electroluminescent display according to a
third embodiment of the present invention.
FIG. 12 is a schematic view for illustrating a method for
fabricating an organic electroluminescent display according to a
fourth embodiment of the present invention.
FIG. 13 is a schematic view for illustrating a transferring
apparatus used for the present invention.
FIG. 14 is a block diagram for illustrating a method for
fabricating an organic electroluminescent display according to
another embodiment of the present invention.
FIG. 15 is a graph for illustrating a sectional energy distribution
of a laser beam applied to another embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 3 is a block diagram for illustrating a method for fabricating
an organic electroluminescent display, and FIG. 4 is a schematic
view of an organic electroluminescent display fabricated according
to a method shown in FIG. 3.
As shown in the drawings, first electrode layers 12 having a
thickness of about 100-500 nm is formed on a transparent substrate
10 by sputtering indium tin oxide (ITO).
An assistant layer (hole transport layer) 14 having a thickness of
about 10-100 nm is formed on the first electrode layer 12 by, for
example, a spin coating process, a dip coating process, a vacuum
evaporative deposition process, or a thermal transferring process.
An R-G-B organic luminescent layer 16 is formed on the assistant
layer 14 by a thermal transferring process. A second electrode
layer 18 intersecting the first electrode layer is formed on the
organic luminescent layer 16.
Here, An insulating layer formed of an organic material such as
polymer photoresist or an inorganic material such as SiO.sub.2, and
SiN.sub.2 may be deposited between the line patterns of the first
electrode. The second electrode layer 18 may be formed by
depositing aluminum through a vacuum evaporative deposition process
at a thickness of about 50-1500 nm.
In addition, for an increase of an efficiency, a material such as
LiF may be disposed between the organic luminescent layer and the
second electrode layer.
In order for forming an organic luminescent layer by a thermal
transferring method, a donor film formed of a base film, a light
absorption layer, and a transfer layer is required, and a desired
pattern of the emission layer is obtained by scanning a laser beam
after disposing the donor film on an upper side of a substrate
provided with the first electrode layer and the assistant layer
In order for fabricate a full colored organic electroluminescent
display, three donor films for the three colors of R, G, and B is
required, and emission patterns of R, G, and B may be obtained by
three times of scanning process on respective donor films.
Emission pattern of an organic electroluminescent display should
show flatness on the surface, high image quality at the edges, and
uniform thickness distribution. Therefore, in order for forming an
organic emission layer by a thermal transferring method, it is
preferable that energy distribution of a laser beam scanned on the
donor film is uniform and shows rapid inclination near the edges
such that width may not fluctuate due to non-uniform sensitivity of
the donor film.
Therefore, it necessitates an alteration of laser beam from energy
distribution of Gaussian shape such that energy is decreased in its
central portion while energy distribution rapidly change near the
edges. For such an alteration of an energy distribution, according
to the present invention, the laser beam may be dithered in a
perpendicular direction with respect to a scanning direction of the
beam, or a single beam composed of a plurality of laser beams
having different energy distribution. The scheme of dithering a
laser beam is first described.
FIG. 5 is a schematic view for illustrating a method for
fabricating an organic electroluminescent display according to a
first embodiment of the present. In the drawing, the reference
numeral 20 indicates a pattern of a organic luminescent layer to be
formed on an assistant layer.
And, the reference numeral 22 indicates a laser beam as a light
source for scanning the pattern 20.
The laser beam 22 moves in an X-direction shown in the drawing
(i.e., from the left to the right in the drawing) along the pattern
20 to perform the scanning process. At this point, differently from
the prior art, while moving in the X-direction, the laser beam 22
dithers in a Y-direction.
By the dithering movement of the laser beam 22, the thermal 10
transferring process is effectively realized even at both edges 20a
and 20b of the pattern 20. The dithering movement is realized by
alternating the advancing direction of the laser beam under the
control of an acousto-optic modulator (AOM).
In addition, the dithering speed is preferably higher than the
scanning speed. In more detail, considering the scanning speed and
the energy distribution, it is preferable to set the dithering
speed at about 100-10,000 KHz.
Although the section of the laser beam 22 may be formed in various
shapes such as a circular or an oval shape, an oval shape is more
preferable. Particularly, in the case that the pattern 20 of the
organic luminescent layer is formed lengthily in a lengthwise
direction as shown in the drawing, it is preferable that the
section of the oval-shaped laser beam 22 is designed to have its
major axis aligned in the scanning direction of the beam, since
energy distribution applied to the pattern 20 may become uniform
over entire portion thereof due to an increase of overlapping ratio
of the beam during scanning.
When the lateral width W of the pattern 20 is 60-150 .mu.m, it is
preferable that the section of the laser beam is oval-shaped having
its major axis of 200-500 .mu.m and its minor axis of 15-50
.mu.m.
As shown in FIGS. 6 to 8, the laser beam performs its scanning
operation along a waveform of a sine wave (see FIG. 6), a saw-tooth
wave (see FIG. 7), or a trapezoidal wave (see FIG. 8). At this
point, the sectional energy distributions of the laser beam 22 for
the waveforms are as shown in FIG. 9.
As shown in FIG. 9, when the laser beam performs its scanning
operating without the dithering movement, the laser beam (i.e.,
Gaussian beam B1) has an energy distribution having an inclination
gently reduced as it goes from the central portion to the edges of
the pattern.
However, the laser beam 22 of the present invention has an energy
distribution having an inclination steeply increased as it goes
from the central portion to the edges of the pattern (See graphs B2
and B3 in FIG. 9 which respectively represent the laser beams
performing their dithering movements in the shape of the sine wave
and the trapezoidal wave).
Based on such energy distributions, it is found that the intensity
of the laser beam 22 of the present invention is not reduced even
at the edges 20a and 20b of the pattern 20 thereby effectively
realizing the thermal transferring process there.
In addition, the laser beam 22 according to the present invention
has similar intensity at its central portion and its edge portion,
and accordingly, surface roughness of the pattern 20 may be
prevented.
That is, when the beam intensity is increased to compensate for the
intensity of the beam edge as in the conventional laser beam B1,
the surface of the pattern becomes uneven. However, the laser beam
of the present invention has the beam intensity throughout its
entire area, there is no need to increase the beam intensity to
compensate for the beam edge. As a result, the flatness of the
pattern can be improved.
In the above-described first embodiment, a single laser beam is
radiated from a single laser unit. However, the present invention
is not limited to this.
That is, the laser beam 22 may be formed in various manners to form
organic luminescent layer by a thermal transferring method, and
another embodiment for the various manners is as follows.
FIG. 10 is a drawing for illustrating a method for fabricating an
organic electroluminescent display according to a second embodiment
of the present invention. According to the present embodiment, That
is, as shown in FIG. 10, plural split laser beams 22 and 22' may be
radiated from a single laser unit (not shown) so that plural
organic luminescent layer patterns 20 and 20' are simultaneously
scanned while dithering the laser beams 22 and 22'.
Preferably, the plural split laser beams 22 and 22' are
synchronized.
When the plural laser beams 22 and 22' are dithered and scanned
synchronously, a plurality of organic luminescent layer patters are
simultaneously formed by one operation.
In addition, differently from the second embodiment, a plurality of
laser beams may be used for forming an organic luminescent
layer.
FIGS. 11 and 12 are drawings for illustrating such a scheme.
Firstly in FIG. 11, plural laser beams radiated from plural laser
units (not shown) are overlapped one another to form a single
overlapped laser beam 32 (in this case, each laser beam has the
same energy distribution), and they are dithered and scanned.
That is, according to a third embodiment of the present invention,
for example, lasers from two laser units are overlapped to be
unified and they are dithered while scanning. According to such a
scheme, beam intensities are doubled relative to laser beam from a
single laser unit, and accordingly, scanning speed may be
increased.
Alternatively, as shown in FIG. 12, plural laser beams 42 and 44
may be radiated from plural laser units (not shown) so as to
perform the scanning operation with different phases without
overlapping.
At this time, the plural laser beams have equal energy
distribution.
In addition, the plural laser beams may be applied to adjacent
organic luminescent layer patterns as shown in FIG. 10 so as to
fabricate organic luminescent display by dithering and scanning.
The plural laser beams are preferably synchronized.
FIG. 13 shows a thermal transferring apparatus used for the present
invention.
Referring to the drawing, a high energy laser beam is radiated from
a light source, i.e., a laser unit 50. A high energy solid laser
such as a Nd/YAG laser or a gas laser such as a CO.sub.2 laser are
used as the light source.
As described above, the radiated laser beam may be either of a
single laser beam radiated from one or more lasers or split laser
beams formed by a splitting of such a single laser beam with equal
intensity by a splitter.
The single laser beam or the split laser beams is adjusted in its
intensity by a modulator 52 and then reach a scanning mirror 56 via
a first lens array 54.
The scanning mirror 56 guides the laser beam to a target position
on the substrate in the X-direction.
The laser beam that has reached the scanning mirror 56 is emitted,
through a second lens array 58, to the donor film 60 on which a
luminescent material is deposited. Then, the luminescent material
deposited on the donor film 60 is transferred to the substrate 62,
only at a portion scanned by the laser beam.
The donor film 60 and the substrate 62 are supported on a stage 64
whose movement is controlled by a computer 66. The computer 66 also
controls the scanning mirror 56 through a scanning mirror
controller 68.
The dithering movement of the laser beam is controlled by the
modulator 52 which is controlled by the computer 66.
In the above description, embodiments are described in connection
with various types of dithering the laser beam. However, according
to the present invention, an organic luminescent layer may be
formed using a single laser beam composed of a plurality of laser
beams of different energy distributions, as shown in FIGS. 14 and
15.
The single laser beam B4 is formed by a composition of a laser beam
B5 having a large size (i.e., having gentle inclination in energy
distribution) and laser beams B6 and B6' having a small size (i.e.,
having steep inclination in energy distribution).
The single laser beam B4 formed as such may have a steep
inclination in energy distribution at a threshold energy, i.e., a
minimally required energy for a transferring, and a resultant
pattern may have enhanced flatness and edge characteristics.
forming an organic luminescent layer using a single laser beam
mixed plural laser beams having a different inclination in energy
distribution
In an embodiment of the present invention, it is preferable that a
poly phenylene vinylene (PPV)-based material or a polyfluorene
(PF)-based material is used for the organic luminescent layer.
While this invention has been described in connection with what is
presently considered to be the most practical and preferred
embodiments, the present invention is not limited thereto. Various
variations may be realized within the appended claims, detailed
description of the present invention, and the drawings, and
consequently, such variations should be understood to be within the
scope of the present invention.
[Effect of the Invention]
As can be seen from the above description of the constitution and
operation of the present invention, according to a method for
fabricating an organic electroluminescent display according to the
present invention, a Gaussian beam is dithered during scanning or a
single beam formed by composition of a plurality of beams having
different energy distributions. Therefore, image formation may be
enhanced at the edges of the organic electroluminescent display,
and quality of a organic electroluminescent layer due to enhanced
flatness of the pattern surface.
* * * * *